The objective of this work is to define the usefulness of nonhuman primates as models for study of three conditions of importance in older humans. There are three projects: 1) Evaluation of the frequency of occurrence of benign prostatic hyperplasia in male primates of different species. This involves studies of morphologic, endocrine and biochemical characteristics. 2) Evaluation of the effects of hypertension and atherosclerosis, common age associated conditions, on the central nrvous system. This involves study of cognitive behavior, cerebral blood flow and cerebral morphology. Study of human subjects parallels the animal study insofar as possible. 3) Evaluation of sexual behavior of male nonhuman primates with severe atherosclerosis in combination with measurement of general gonadal steriods. Pelvic and genital vessels will be examined at necropsy.